The use of a two-stage compressor reciprocating in a cylinder and on a stationary member is old as shown in U.S. Pat. No. 13,645 Re. However, the prior art air compressor allows air trapped between the piston and the stationary member to be vented to the atmosphere, which while satisfactory for air, is totally unacceptable for compressing a toxic, explosive, or expensive gas such as natural gas.
The present invention is directed to an improved two-stage gas compressor which avoids leakage of gas from the compressor and avoids unnecessarily compressing gas in the interior of the piston.